Re: [Bugme-new] [Bug 11448] New: NFS client has inconsistent write flushing to non-linux serversa

[Doug Hughes <doug-rDJHdQPhaF8@public.gmane.org>]

Peter Staubach wrote:
> J. Bruce Fields wrote:
>> On Thu, Aug 28, 2008 at 01:27:53PM -0700, Andrew Morton wrote:
>>  
>>> (switched to email.  Please respond via emailed reply-to-all, not 
>>> via the
>>> bugzilla web interface).
>>>
>>> On Thu, 28 Aug 2008 11:41:08 -0700 (PDT)
>>> bugme-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r@public.gmane.org wrote:
>>>    
>>>> NFS client writes to Sun Solaris 10 U4 server. at some point in 
>>>> time, there is an empty portion of the output file from the
>>>> writer containing missing data (shows as NULL bytes from another 
>>>> NFS client
>>>> issuing a tail -f on the file being written). confirmed that the 
>>>> file as exists on the NFS server is sparse, missing bytes
>>>> (not necessarily multiple of 512 or 1024, one sample is a gap of 
>>>> 3818 bytes,
>>>> another is 1895 bytes, another is 423 bytes)
>>>>       
>>
>> Seems like something that could happen if for example two write rpc's
>> got reordered on the network.  That's not necessarily a bug--the nfs
>> client isn't required to wait for confirmation of every previous write
>> before sending the next one.
>>
if two RPCs got reordered on the network, and they encompass all the 
data, then there shouldn't be any missing data. It seems to me like 
pieces of data are just being skipped, for whatever reason, but I 
haven't exhaustively examined the NFS network data.

>> However if the client isn't flushing dirty data to the server before
>> returning from close, then that's a violation of NFS's close-to-open
>> semantics:...
>>
this is not confirmed yet. No solid cases of data not being present 
after close.
>>  
>>>> if you do a read of the entire file from the NFS client doing the 
>>>> writing, it
>>>> causes the non-flushed writes to be instantly flushed to the server 
>>>> followed by
>>>> a NFS3 commit operation. The data then can be seen on all other NFS 
>>>> clients.
>>>>
>>>> If you do an open of the file alone, no flush
>>>> if you do an open and a close, no flush
>>>>       
>>
>> ... so this "close, no flush" could be a bug (depending on who is doing
>> that close when--I don't completely understand the described situation).
>
> I suspect that this last might depend upon 1) what options were used
> when the file system was mounted and 2) how the file was opened.  The
> flush-on-close wouldn't be needed if the file was opened read-only.
>
no special options on open. Here are the mount options:
retry=1000,tcp,noatime,nosuid,nodev,dirsync,timeo=100,rsize=32768,wsize=32768
,hard,intr


> It seems a little odd that the holes aren't page aligned or page
> sized multiples.
>
indeed. and the time for them to actually get to the server is 
indeterminate (days is not uncommon. We have not as yet confirmed that 
some of the data never gets sent to the server until close)

> What application is being used to generate the file which is showing
> these holes?
>
namd and some custom code developed in-house for chemistry research (at 
the very least)